1. Field of the Invention
The present invention pertains to the art of induction cooking appliances and, more particularly, to an induction cook top appliance with a heat management system, such as a fixed or adjustable ventilator and an adjustable blower.
2. Discussion of the Related Art
Induction cooking, though long a favorite method of cooking in other parts of the world, has only recently become popular in the United States due to its high energy efficiency. Further, induction cooking is more efficient than gas or radiant heat because the cooking elements, i.e., electromagnetic coils, or hobs, are powered by induction generators that induce high levels of current in a pot placed on the cook top, thus heating the pot because of its high electrical resistance. The food or liquid in the pot is heated more quickly because very little heat is lost around the sides of the pot, i.e., the vast majority of heat is transferred directly to the contents of the pot.
Often, it is considered beneficial to utilize some type of ventilation system to evacuate the airborne contamination, either upward through a venting hood or downward into a draft flue. In kitchens, most known venting arrangements take the form of a hood which is fixed above a cooking surface and which can be selectively activated to evacuate the contaminated air. Downdraft vent arrangements are also widely known in the art wherein a cooking surface will incorporate a vent opening that is positioned between different sections of the cooking. During induction cooking, the heated pot may radiate heat down into the chassis or housing of the cook top, which can be of the drop in or slide in design as well as free standing. Often times, some type of internal ventilation system is used to evacuate the air in the chassis either upward through venting slots above the cook top or counter or downward into the cabinet.
The vertical distance between the cooking surface and a vent hood is typically fixed between 24 and 30 inches. When in an operating position, downdraft vent arrangements known in the art are also limited in this respect. Depending upon the food being cooked and even the particular height of the individual doing the cooking, it may be desired to vary the distance between the cooking surface and the vent hood. On a cooking surface, it is considered beneficial to arrange a vent closer to the cooking surface in order to increase the removal of contamination. On the other hand, it is often desirable to raise a vent hood relative to a cooking surface in order to more easily access different portions of the cooking surface. Typically, the internal components in the main housing are cooled by moving the heated air out of the housing. However, existing cooling systems do not account for the temperature of the incoming air, i.e., the systems are directed toward air removal from the inside the housing without considering the surrounding air temperature. Further, many existing systems re-circulate the previously expelled heated air back into the housing cavity, thereby increasing the temperature inside. This may result in elevated temperature levels in the housing that may cause component failure and/or reduced cooking performance.
Downdraft blowers are multiple speed fans, having a low speed and a high speed. Blowers are typically controlled by mechanical multi-position switches, potentiometer, or rheostat-type controls, which set the speed of the fan. For removal of normal cooking odors, steam, and other effluents and contaminates, low speed operations of the downdraft blower have been adequate. However, when using such items as a grill, a blower set at high speed has been better able to withdraw all of the grease-laden air from a kitchen and duct it to the outside environment. In cooking systems, such as cook tops and grills with optimized proximity ventilation, cooking gases, vapors, and odors are drawn into an exhaust inlet and are better exhausted into the atmosphere. Usually, the exhaust inlet is located adjacent the cooking surface and the inlet to a flow path which serially includes a plenum, a blower, an atmospheric exhaust, and interconnecting ductwork. The flow path to the atmosphere normally extends through a wall or floor of the room in which the cooking system is located, but can also be exhausted into a room, if filtered.
The blower/fan is frequently a separate unit from the rest of the cook top and is installed prior to the installation of the unit into a counter top. Some blower systems are provided with a pair of brackets, which permits the selective mounting of the blower to the floor or the appliance itself for discharge either through a wall or through the floor, as required by the installation. Conventional downdraft venting system configurations with an exhaust air inlet located at cook top level work well with electric surface units. However, when used in combination with gas on glass surface units, the downdraft-induced air flow at the cook top surface tends to interfere with the gas flame.
A cook top using induction heating for cooking purposes is normally constructed of a metal housing supporting a glass or other cooking surface upon which there is located a number of induction heating coils sandwiched in between. The housing normally contains an electronic package for use in supplying electric power to the coils. This package consists of a group of interconnected electronic components. The package is connected to the coils with wires that are mounted within the housing. This package is sometimes called the generator and the entire induction system is sometimes called a cooking cartridge.
Because of the heat generated by the induction coil package and the electronic circuitry for operating the induction coil, both of which are located below the cooking surface within the cooking cartridge, it is necessary to provide some form of cooling for the induction coil and its associated circuitry. The fan has been found to be the least expensive and most reliable cooling solution. The known drawback here, though, has been the sensitivity of the air flow, disruption of which causes failure or reduced energy for operation of the induction system.
In order to operate for a prolonged period without the induction system breaking down/turning off, it is necessary then to use a fan that circulates air throughout the interior of the cook top housing so as to maintain the proper temperature for the electronic components employed. Failure to keep the generator cool results in loss of power to the cooking product all the way to a complete unit shutdown. Normally, such a fan or blower is connected into the circuit used to supply power to the electronic components and, thus, is automatically turned on each time the cook top induction element/generator is turned on. However, to avoid overheating, the fan remains on after shutdown of the cooking elements so that heated air within the cook top housing can be removed until a proper safe heat level is obtained.
While the use of a fan in this manner is desirable in preventing heat-caused damage to the electronic components employed, it is also considered a disadvantage. The use of a fan has two issues when used for cooling an induction cook top. When a fan is used in this manner, noise associated with the fan's operation is present whenever a cook top with induction of the type is used. Many users find this noise to be objectionable. Further, the use of a fan alone is considered a problem because if air flow is blocked, the unit must be completely shut down for safety reasons. However, a user does not take into consideration whether or not there is heat buildup present within a housing, rather only noting that the unit failed to operate.
Although it is possible to use other methods to keep the temperature down, e.g., by the use of thermostats and various related known temperature sensing apparatus for controlling the flow of current in an electrical circuit, it is known that such expedients are undesirable for any of a variety of reasons, including effectiveness, cost, and reliability.
It has also been shown that a particular air flow path may be helpful, e.g., whereby an internal fan draws cooling air directly into a cooking cartridge, across the induction heating components, out an opening in the bottom of the cartridge, and then exhausts the heated air above the cook top surface through a gap all around the cartridge between a support flange on the cook top surface. There also has been development of a modular cooking cartridge where the internal fan draws cooling air into the interior of the cooking cartridge through the cartridge top, over the induction heating components, and out through exhaust openings in the cartridge top by way of an air flow path, including an opening in the cooking cartridge container and an exhaust conduit formed by the cartridge container and an auxiliary housing fixed to the container.
As noted, many conventional cook tops often have integrated downdraft ventilators. Present designs are long rectangular boxes extending below the glass or metal cook top. They extend below the cook top housing as much as 30 inches below the surface or counter top. Attached to this box or plenum is the blower assembly extending outward from the box. The plenum does not, in some cases, provide any sealing to prevent the drawing of air from the box. Included in the typical downdraft assembly are: the blower housing assembly, squirrel cage housing assembly, centrifugal wheel, blower motor assembly, plenum chamber assembly, and a passage between the cook top and the plenum chamber for removal of air from the top surface of the appliance. The box is often of a single-walled or a double-walled construction, if you include the cook top box/housing with insulating air in between the plenum and cook top housing. An opening is provided to the interior of the box for exhausting. The centrifugal type fan/blower may be housed in the squirrel cage housing assembly and attached to the plenum. Such a single fan blower may also be attached to the side of the plenum with air flow at 90 degrees from the side of the plenum.
Blowers have been generally designed to draw air downwardly with the use of a centrifugal type fan, and thus remove contaminated air from a cook top surface, remove the interior air of the box, and exhaust it outside or return to the room. A centrifugal fan creates higher pressures than that of an axial flow fan. In such conventional systems, the air flow stream is pulled from the front and sides of the work area to the middle where the ventilator is. The air stream has to then turn 90 degrees downwardly, once inside the plenum chamber. The air stream has to then turn 90 degrees again into a small diameter opening when compared to the size of the ventilator's plenum chamber. The air stream then enters the blower flow efficiency and usually is redirected downwardly again for exhausting. With all this bending of the air stream, air is lost. Thus, large amounts of draw/vacuum/suction are needed to overcome all these losses. With the need for more draw/vacuum/suction comes a larger fan/blower motor, which increases costs, noise, size, and weight.
Present centrifugal fans consist of a wheel with small blades on the circumference and a shroud to direct and control the air flow into the center of the wheel and out at the periphery. The blades move the air by centrifugal force, literally throwing the air out of the wheel at the periphery, creating a vacuum/suction inside the wheel. There are two basic design types of wheel blades in centrifugal blowers—forward curved blades and backward inclined blades.
Forward curved wheels are operated at relatively low speeds and are used to deliver large air volumes against relatively low static pressures. However, the light construction of the forward curved blade does not permit this wheel to be operated at speeds needed to generate high static pressures. Thus, this type is generally not used in downdraft ventilators.
The backward inclined blade blower wheel design has blades that are slanted away from the direction of the wheel travel. The performance of this wheel is characterized by high efficiency, high cubic foot per minute (CFM) operation and is usually of rugged construction making it suitable for high static pressure applications. The maximum static efficiency for these types is approximately 75% to 80%. A drawback to this type is that it must be designed for twice the speed, which increases the cost of the unit.
To date, axial flow fans are not used for such cook top venting. Myths of why include: they cannot provide the static pressures needed for drawing/vacuum/suction, size, and spacing requirements. Axial flow fans come in three basic types of fans. The propeller fan (e.g., the household fan), the tube axial fan, and vane axial fan (cross flow or tangential). The first of these is the most familiar. The propeller fan consists of a propeller blade and a so-called “aperture” to restrict blowback from the sides. Without the aperture, the fan is not truly a propeller fan, since it cannot positively move air from one space to another. The aperture is usually sheet metal/plastic designed to fit closely around the periphery of the propeller. The tube axial fan (found in computers) is literally a propeller fan in a tube. In this case, the tube replaces the aperture. The tube axial fan generally increases flow quantity, pressure, and efficiency due to the reduced air leakage at the blade tips. The vane axial fan (cross flow or tangential) is a tube axial fan with the addition of vanes within the tube to straighten out the air flow. Here, the air flow changes from helical flow imparted by the propeller into a more nearly straight line flow and in the process increases the suction or draws pressure and efficiency while reducing noise. In general, the propeller fan operates at the lowest pressure. The tube axial fan is somewhat higher, and the vane axial fan supplies the highest-pressure output of the three. Vane axial fans are noted for use when available space for installation is limited, such as that of computers. Static efficiencies of 70% to 75% are achieved with vane axial fans. The CFMs and static performance ranges of the vane axial fan are similar to that of a centrifugal fan. Horsepower requirements are about the same for both designs.
The present downdraft ventilator designs also present problems when integrated into a cook top. Because of the low profile, spilled food and liquids can enter the grate, and removal of the items that are not captured by the filter cannot be removed easily. This is due to the required depth of the plenum and the narrow box size.
The present design of ventilators is also often large and bulky. Examples would be downdraft ventilators built into a cabinet or used on an island countertop. There, the space below the unit is not available for a user to use for storage due to the centrifugal blower below and the size of the plenum presently used. Large size also limits the downdraft ventilator from being placed in other areas or used with other products below the cook top. This also limits the downdraft ventilators from being used as a freestanding unit, as a mobile unit, used in a cabinet (e.g., suspended), or in areas that do not have the ability to support a large structural frame below.
A document from Osaka Gas Company entitled “Research on Required Exhaust Flow Rate in Commercial Kitchens in the case of Gas-Fired and Induction-Heating Cooking Equipment” illustrates some problems when using ventilators for removal of contaminated air. For example, with the use of induction heating cooking stoves, even a weak side draft caused the cooking contaminants to move outside the exhaust vent because there was not enough energy to raise the air up for the collection to take place. These results show that when induction-heating cooking equipment was used in a real commercial kitchen environment where the room air was disturbed, oil smoke or other cooking contaminants were not fully removed by the exhaust vent.
Present day induction coils are made to a critical temperature of 200° C. beyond which they undergo damage to the insulation between the wires. There have been attempts to do other things in the coils, especially at the center of the coil, by providing for a temperature sensor, for example, a thermistor, to prevent the overshooting of temperature limits. However, this type of localized sensor has very localized action and does not take into account the entire surface area of the generators/inductor. If the sensor does not work properly, there are situations in which the critical temperature may be reached and even exceeded causing damage. This is especially so when an empty pan is placed above the element supplied with current, or when food to be cooked has to be deep-fried. The results of these attempts ended with fans being added to keep the temperature in the proper operating range.
The prior art primarily is directed to controlling the operation of an internal electric fan for cooling the induction heating cooking apparatus, but it fails to address the flow of ambient air outside the housing.
The below-referenced U.S. patents disclose embodiments that were at least, in part, satisfactory for the purposes for which they were intended. The disclosures of all the below-referenced prior United States patents in their entireties are hereby expressly incorporated by reference into the present application for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art.
For example, U.S. Pat. No. 4,549,052 discloses an internal cooling system for an induction cooking cartridge. This system includes an internal fan for cooling the various induction heating components. The cooking cartridge features an airflow that enters a mounting recess in at least two areas and enters at both the top and bottom of the cartridge cavity. The airflow is directed over the induction heating circuitry for cooling and is exhausted through the fan to an exhaust conduit. However, this system does not address the issue of the surrounding air intake and the temperature or quality of the air that is brought back into the housing for cooling.
U.S. Pat. No. 4,191,875 is directed toward controlling an internal electric fan for cooling an induction heating apparatus. It discloses a fan for circulating air through an induction cook top housing and maintaining the temperature of the electronic components. A thermistor is located near the induction heating apparatus and controls the operations of a fan. The speed of the electric fan is proportional to the degree of induction heating of the heating elements. The thermistor is in series with a variable resistor and a capacitor. When the capacitor is charged to a predetermined voltage through the thermistor and variable resistor, it will fire a signal through a component to allow current to flow through an electronic component and operate the fan motor. This system also includes a plurality of air inlets and outlet holes in the walls of the housing so that the fan randomly pulls air in one side and exhausts out the other side of the housing after passing over the induction heating apparatus. However, this system relies upon the critical factor that the airflow must be undisturbed in cooling.
U.S. Pat. No. 4,415,788 describes an induction cartridge having an internal forced air cooling system where a fan draws air into the cartridge cavity, circulates it around the induction heating components, and exhausts it out an opening in the bottom of the cartridge. This patent discloses exhausted air being returned to the kitchen environment through an exhaust gap around the periphery of the cartridge between the housing top and the bottom of a support flange. It is also stated that to protect the air stream, a separate drop in cartridge be made that isolates the induction elements from any other source of blockage. An induction hob cartridge contains a fan integrated into the hob assembly for cooling the electronics. The problem with this design is that the cartridge does not take into account the exhausted air or the air that is brought into the system. Specifically, the heated air is exhausted out the top edges and may be drawn back into the unit.
In another example, U.S. Pat. No. 4,431,892 discloses an induction cook top as a cartridge being fitted into a recess in a housing. The main innovation is an attempt to ventilate the interior of the cartridge using a ventilation system housed in the main body. The cartridge has openings on the side and top for air to pass through once connected to the holes in the down draft ventilator. However, this design is flawed because air that is drawn in will take the path of least resistance, i.e., the air would not be drawn effectively from the cartridge. Without proper air flow, the generator in the induction cartridge would overheat which may result in component failure or destruction.
In U.S. Pat. No. 4,100,964, an induction ventilation system featuring a liquid cooling system for removal of heat is disclosed. This system can be large, complex, and take up large amounts of space. Moreover, this system does not treat the incoming air. Thus, the exhausted heated air may be returned back into the cavity of the housing.
In U.S. Pat. No. 4,549,052, an induction hob cartridge contains a fan integrated into the hob assembly for cooling the circuitry. This system includes an internal fan for cooling the various induction heating components. The cooking construction has a unique air flow, which enters a mounting recess in at least two areas and enters the cartridge cavity at the bottom and the top. The air flow is directed over the induction heating circuitry for cooling and is exhausted through the fan to an exhaust conduit. This design does not take into account where the air is exhausted and the potential of drawing the exhausted air back into the cavity. Specifically, the heated air is exhausted out the top edges and may be drawn back into the unit if the exhausted air is not moved away from the intake vents for the cartridge.
Another approach to protecting the components within induction cooking was illustrated in U.S. Pat. No. 3,710,062. This invention includes a relatively complex thyristor gating circuit for precisely establishing the recharge period between conductive cycles of the inverter to cause the reapplied forward voltage across the thyristor to be insensitive to the loaded or unloaded condition of the work coil. However, it was found that this approach was incapable of protecting the inverter when loaded with a highly conductive utensil due to the heat buildup. A second circuit was illustrated in U.S. Pat. No. 3,775,577, which was included in the appliance based upon establishing a pedestal of predetermined length initiated by the start of a conductive cycle and assuring that commutation occurred within the period set by the pedestal. Again, issues still remained as to the cooling requirements needed with different types of loads.
Other known induction cooking appliances in prior patents, (e.g. U.S. Pat. Nos. 3,781,505 and 3,820,005) have attempted to protect the inverter by utilizing constant duty cycle controls for measuring the conductive interval of the inverter and adjusting the length of the recharge period to maintain an approximately constant duty cycle. As such, controls increase the operating frequency in response to a decreased conductive interval (as is normally caused by loading of the inverter) and they are not particularly suited to protecting the inverter from improper loads. In certain instances, presenting a highly conductive utensil to the work area causes a substantially shortened conductive interval, which, in turn, causes the constant duty cycle control to raise the operating frequency even higher, thus further aggravating the situation. The end result is increased temperature and the need for more air flow to cool the unit down.
Air flow systems have been generally utilized for control protection purposes in induction and other cook tops. For example, U.S. Pat. No. 3,859,499 discloses an air flow system for heat-cleaning ranges in which room air is drawn through air inlets located along the sides and top of an oven opening. The air passes through a space between the range's outer casting and the inner oven cabinet. A blower draws air into the upper air flow passageway during an oven heat-cleaning cycle. The blower exhausts air to the atmosphere through a vented splash panel.
Therefore, there exists a need for a state of the art indoor or outdoor induction cook top with heat management system to control the heat generated by the components, electronic controller, mechanical controls, or the induction generators, and to provide precise temperature control and efficient heat removal without drawing exhausted air back into the system. Further, there exists a need for an induction cook top having a smaller depth for ease of extraction and no venting above the counter. There exists a need for the user to be able to view/see the operation, functions, and view the codes on the cook top. There also is needed a new cook top construction such that can be used in limited spaces and places. Further, there is a need for a proper vent design so as to efficiently remove undesired heated air from the housing of an induction cook top appliance. There is also a need for controls to be less susceptible to the environment. Additionally, there is a need for a remote control, a need to accurately apply and control heat output as it is returned to the room, and a need for a new design that can be used in a variety of places and spaces.